US3549824A - Magnetic recording head having constant-width recording gap subjected to decaying amplitude bias - Google Patents

Magnetic recording head having constant-width recording gap subjected to decaying amplitude bias Download PDF

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Publication number
US3549824A
US3549824A US727965A US3549824DA US3549824A US 3549824 A US3549824 A US 3549824A US 727965 A US727965 A US 727965A US 3549824D A US3549824D A US 3549824DA US 3549824 A US3549824 A US 3549824A
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United States
Prior art keywords
signal
bias
magnetic
magnetic recording
recording head
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Expired - Lifetime
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US727965A
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English (en)
Inventor
Arthur Edward Brewster
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STC PLC
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International Standard Electric Corp
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Priority claimed from GB50574/66A external-priority patent/GB1183587A/en
Application filed by International Standard Electric Corp filed Critical International Standard Electric Corp
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Assigned to STC PLC reassignment STC PLC ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: INTERNATIONAL STANDARD ELECTRIC CORPORATION, A DE CORP.
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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/48—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed
    • G11B5/49—Fixed mounting or arrangements, e.g. one head per track
    • G11B5/4907—Details for scanning

Definitions

  • ABSTRACT A magnetic recording head having a single magnetic recording gap extending across the width of a recording medium. To record successively across the width of the medium, a repetitive, diminishing AC signal is applied to a magnetic coil mounted at one side of said medium and the resulting bias flux is applied to said medium via either said gap or a separate biasing gap.
  • the separate biasing gap is arranged beside the recording gap, in another it is opposite the recording gap and in a third, the recording medium itself passes through the biasing gap.
  • PATENIEDDEBZZISYB 35491824 SHEET3UF5 N N M m a o ⁇ ooc Q was:
  • the invention relates to a magnetic recording head.
  • Magnetic recorders storing signals at high-speed and/or at a high packing density frequently resort to the placement of successive signal elements transversely across the width of the tape or other storage medium, i.e. at right angles to the directionof tape motion. This has the-advantage of reducing the actual tape velocity but requireseither a multiplicity of heads with associated switching circuits or the mechanical transverse movement of a single head.
  • An object of the present invention is to provide an improved magnetic recording head 'for recording intelligence on a recording medium of the type in which the signals are recorded transversely across the width of the medium (at an 7 angle to the direction of motion of the medium).
  • FIG. IA shows a cross-sectioned end elevation of a diagrammatical representation of the magnetic recording head according to the invention
  • FIG. 18 shows .a side elevation of a diagrammatical representation of the magnetic recording head according to the invention and as shown in the drawing according to FIG. 1A; 7 I
  • FIG. 2 shows an AC bias signal that may be applied to the magnetic recording head shown in the drawings according to FIG. IA and FIG. 1B;
  • FIG. 3 shows a rectangular hysteresis loop for the pole pieces of the magnetic recording head and/or the material on which the magnetic recording head shown in the drawings according to FIG. IA and FIG. 18 records;
  • FIG. 4A shows a cross-sectioned end elevation of a diagrammatical representation of another arrangement for.
  • FIG. 4B shows a side elevation .of a diagrammatical representation of the magnetic recording head shown in the FIG. 6A shows a cross-sectioned end. elevation of a diagrammatical representation of a further arrangement for the magnetic recording head according to the inventiomand DESCRIPTION OF THE PREFERRED EMBODIMENTS
  • FIG. 1A a cross-sectioned end elevation of a diagramrnatical representation of the magnetic recording head according to the invention is shown and comprises an AC bias winding 1 which is wound on a former 2 which is terminated at each end thereof at the terminals 10 and 11, pole pieces 6 and 7 which are made of a high coercivity magnetic material having a rectangular hysteresis loop M as shown in the drawing according to FIG.
  • a single recording gap 18 which extends the full width of the recording medium 9, for example, a magnetic tape or other magnetic storag'emedium as shown in the drawing according to FIG. 1B, and a signal winding 8 which is shown as a single wire and which as shown in FIGS. 1A and 18 passes through an aperture 16 which is provided between the pole pieces 6 and 7.
  • the side members 5 which also support the former 2, the flanges 3 of which are spaced from the side members 5 by means of the spacing members 4, are made of a material which provides a saturable magnetic path for the AC bias signal ap plied by way of the AC biasing winding 1 therebylimiting the bias amplitude in the recording gap 18 at high bias amplitudes.
  • pole pieces 6 and 7 made of a soft material which is defined as a material which does not retain magnetism permanently but loses most of it when the magnetizing field is removed, may be employed for the magnetic recording head according to the invention in which case the recording medium 9 would need 'to be of a high-coercivity magnetic material having a rectangular hysteresis loop.
  • both the pole pieces 6 and 7 and the recording medium 9 may be made of a high-coercivity magnetic material having a rectangular hysteresis loop, the main criterion being that the closed loop magnetic path should have a rectangular hysteresis loop.
  • the AC bias signal applied by way of the terminals 10 and 11 to the AC bias winding 1 which is shown in the drawing according to FIG. 2 is an oscillatory waveform having a frequency which is several times higher than the highest frequency of the signal waveform which is to be recorded on the recording medium 9.
  • the AC bias signal gradually decays from a maximum value to a minimum value over a period of timewhich is determined by the period of time the signal to be recorded on the recorded medium 9 appears across the magnetic recording head.
  • the bias flux formed by the AC bias signal follows a path having a reluctance which reduces gradually from a maximum value at position A to a minimum value at position C due to the positioning of the AC bias winding 1 relative to the recording gap 18.
  • the pole pieces 6 and 7 are of a soft material and the recording medium 9 is of a magnetic material having a rectangular hysteresis loop then when the AC bias signal is at maximum amplitude i.e. position A, the bias field is sufficient to sweep the rectangular hysteresis loop of the recording medium 9 i.e.
  • the AC bias is insufficient to sweep the rectangular hysteresis loop of the recording medium 9 between the positions A and B, but is still sufficient to sweep the rectangular hysteresis loop of the recording medium 9 between the positions B and C.
  • the AC bias threshold i.e. the AC bias signal amplitude which is only just sufficient to sweep the rectangular hysteresis loop of the recording medium 9 to cyclically magnetize it, is thus at position B.
  • At minimum AC bias signal amplitude i.e. at position C, on the AC bias signal is thus at position B.
  • the AC bias is barely sufficient to sweep the rectangular hysteresis loop of the recording medium 9 at position C.
  • the bias threshold mentioned in the preceding paragraph can be moved anywhere alongthe magnetic recording head between the position A and C.-In order to understand the mechanism involved consider only a small strip of the recording medium 9 positioned anywhere between the positions A and C of the magnetic recording head shown in the drawing according to FIG. 1B
  • the state of the smallstr'ip of the recording medium 9 hereinafter referred to as a domain will be unchanged.
  • the domain is swept through its rectangular hysteresis loop by the AC bias signal, which affacts it with diminishing amplitude i.e.
  • the domain is cycled through a succession of minor hysteresis loops as the amplitude of the AC bias signal decreases until finally the domain settles out at position on the rectangular hysteresis loop 14 shown in the drawingaccording to FIG. 3 which is the neutral state, at a time t; which is later than the time At and after the time t the domain will be left in a demagnetized state until the next AC bias signal is applied thereto. 2
  • the maximum amplitude of the signal to be recorded which would in practice be a serial signal waveform must be below a level at which any recording could take place i.e. as shown in FIG. 3 the magnetizing force l-ll due to the maximum signal to be recorded should never exceed the coercivity value for the recording medium 9 (it must be kept below the value of the knee 12 of the rectangular hysteresis loop 14 shown in the drawing according to FIG. 3.) incoming If the states of the domain or domains mentioned in a preceding paragraph are now considered when the signal to be recorded is present in the signal winding 8, then at the time t, the domain will only be influenced by the signal waveform, which as previously stated is incapable of changing its state of magnetization.
  • the definition (elements per unit distance) of the signal, as recorded transversely across the storage medium, is not inherently defined by any mechanical or magnetic discontinuity in the magnetic recording head structure.
  • the definition will be determined by the rate of change of the applied signal in relation to the velocity of the scanning AC bias signal waveform, for example, at a scanning velocity of 8 inches per millisecond a 400 kc./s. signal waveform should be recorded with its successive half-cycles each 0.01 inches wide.
  • the recorded definition will also be governed by the frequency of the scanning AC bias signal waveform. It has been shown in a preceding paragraph that a transition to the mark condition can only coincide with a positive-going halfcycle of the AC bias signal waveform. Similarly, the space transitions are confined to the negative-going half-cycles. Hence the true positions of the recorded signal transitions will be distorted to coincide with the phase of the scanning AC bias signal waveform, the possible error lying within the spatial equivalent of plus or minus one half-cycle of this waveform. The significance of this effect can however be minimized by ensuring that the frequency of the scanning AC bias signal waveform is made several times higher than the highest frequency of the signal to be recorded.
  • FIGS. 1A and 1B utilizes the same gap i.e. the recording gap 18, for both the signal which is to be recorded and the AC bias signal this need not be the case.
  • a third pole piece could be used to provide another gap for the AC bias signal, for example as shown in the drawings according to H618. 4A, 45, 5A and 5B or a separate gap could be provided for the AC bias signal, for example as shown in the drawings according to FIGS. 6A and 68.
  • the arrangements shown in FIGS. 4A, 48, 5A, 5B, 6A, and 6B operate in exactly the same manner as the arrangement shown in FlGS. 1A and 1B.
  • FIGS.- 4Aand 413 a cross-sectioned end elevation and a side elevation of another arrangement of the magnetic recording head according to the invention are respectively diagrammatically illustrated.
  • the recording gap 18 is provided in a pole piece 13 which together with a pole piece 21 forms another gap: 17 for the AC bias signal (shown in FIG. 2) applied by way of the AC bias winding 1 which is wound on a former 2 and which is terminated at each end thereof at the terminals and 11.
  • the pole pieces 13 and 21 support the former 2, the flanges 3 of which are spaced from the pole pieces 13 and 21 by means of the spacing members 4,iand the signal winding 8 which is shown as a single wire, passes as shown in FIGS. 4A and 48 through an aperture 16 which is provided in the pole piece 13. a i
  • the magnetic recording heads shown in FIGS. IB and 4B are generally the same in that the AC bias winding assembly is positioned relative to the recording gap 18 and the gap 17 such-that the bias flux formed by the AC bias signal follows a path'having a reluctancewhich reduces gradually from. a maximum value at position A to a minimum value at position C.
  • the pole pieces 13 and 21 may either be made of soft" material, in which case the recording medium 9 would need to be of a high-coercivity magnetic material having arectangular hysteresis loop, or a high-coercivity magnetic material having a rectangular hysteresis loop.
  • both the pole pieces 13 and 21 and the recording medium 9 may be made of a high'coercivity magnetic material having a rectangular hysteresis loop, the main criterion being that the closed loop (shown in FIG. 2), applied by way. of the AC bias winding 1 which is wound on a former 2 and which is terminated at each ,end thereof at the'terminals I0 and 11.
  • the pole pieces 19 and support the former 2 as shown in the drawing according to FIG. 5B.
  • the flanges 3 of the'former 2 are spaced from the pole pieces19 and 20-by means of the spacing members 4, and the signal winding 8 which is shown as a single wire, passes as shown in FIGS; 5A and'SB through an aperture 16 which is provided in the pole piece 19.
  • the pole pieces 19 and 20,, as shown, in FIG. 5A are generally wedge shaped and the AC bias winding assembly is positioned relative to the recording gap 18 and the gap 24, i.e. between the pole pieces 19 and 20, which both extend between the positions A and C, such that the bias flux formed by the AC bias signal follows a path having a reluctance which reduces gradually from a maximum ,value at position A to a minimum value at position C.
  • the material used for the pole pieces 19 and 20 and the recording medium 9 must be such'that the closed loop magnetic path should have a rectangular hysteresis loop similar to the one shown in FIG. 3.
  • FIGS. 6A and 63 a cross sectionedend elevation and a side elevation of a further arrangement of the magnetic recording head according to the invention are respectively diagrammatically illustrated.
  • the recording gap 18 is provided in a pole piece 22 and a separate gap having. its own magnetic circuit is provided for the AC pieces 23 by means of the spacing members 4, and extend the full width of the recording medium 9 as does the pole piece 22.
  • the signal winding 8 which is shown as a single wire, passes as shown in FIGS. 6A and 68 through anaperture 16 which is provided in the pole piece 22.
  • section of the magnetic recording head is generally the same as the magnetic recording head-shown in FIGS. 1B and 4B in that the AC bias winding assembly is located and positioned relative to the gap 25 such that the bias flux formedby the AC bias signal follows a path having a reluctance which reduces gradually from a maximum value at position A to a minimum value at position C.
  • the pole piece 22 has a generally constant cross section throughout.
  • the material usedfor the pole piece 22 and the recording medium 9 and the material used for the pole pieces 23 and the recording medium 9 must be such that the closed loop magnetic paths formed thereby should have a rectangular hysteresis loop similar to the one shown in FIG. 3.
  • the serial signal waveform to be magnetically recorded on the length of the recording medium 9 immediately below the recording gap 18 of the magnetic recording head according to the invention is fed through the signal winding 8, the direction of propagation being from position A to position C, and the individual elements of the serial signal waveform are magnetically recorded at different positions along this length due to the AC bias signal as its amplitude progressively decreases.
  • the magnetic recording medium 9 is moved by appropriate means such that the next length of the recording medium 9 onto which the next serial signal waveform is to be recorded is positioned beneath the recording gap 18 of the magnetic recording head.
  • the next serial signal waveform may be applied to the signal winding 8 and the next AC bias signal may be simultaneously applied to the magnetic recording head shown in FIGS. 1A and 11B.
  • the magnetic recording medium 9 could be moved continually instead of intermittently relative to the magnetic recording head according to theinvention.
  • a synchronizing pulse interposed between any two serial signal waveforms which are to be recorded on adjacent strips of the recording medium 9 causesthe AC bias to return to maximum amplitude at the correct instant and ensures that the previous recording is not erased.
  • the recording process is not dependent upon a critical amplitude of the serial signal waveform, since the recording takes place when the AC bias signal decays towards zero. It is, however, important to ensure that when the position A on the magnetic recording head is reached, the amplitude of the leading cycle is still sufficient to sweep the recording :medium 9 through its major rectangular hysteresis loop despite attenuation effects due to the flux path formed by the side members 5.
  • the pole pieces '23 which form the gap 25 support the former 2, the flanges 3 of which arespaced .from the pole' image is then developed by passing the printing drum through a powder applicator which contains a powder that is attractive to the electromagnetically formed image.
  • the powder particles are attracted to the surface of the drum and adhere to the electromagnetically formed pattern.
  • the drum surface then comes in contact with a moving strip of paper which has the same linear velocity as the drum surface.
  • a pressure roller presses the paper against the drum, and the powder pattern is transferred under pressure from the drum surface to the paper surface.
  • therr'hal fixing agent for example, resin or wax
  • the powder formulation so that the pattern may be fixed" by the application'of heat subsequent to pattern formation, therefore the paper strip after passing between the printing drum and the pressure roller is passed through heating means wherein the powder pattern is thermally bonded to the surface of the paper strip.
  • the printing drum is of the order of 8 inches wide and it may be required to record, say 800v individual elements across the 8-inch width.
  • the width of the pole pieces on the magnetic recording head and thereby the width of the recording gap would therefore need to be 8 inches.
  • the length of the recording gap i.e. the separation between the pole pieces, might be, say, 0.01 inches. If at a given instant, only 0.01 inches of the head width were activated, the effective record region would be limited to an area of 0.01 X 0.01 inch and it wouldbe possible to define 8 such regions across the width of the magnetic recording head according to the invention.
  • FIGS. A and 5B and FIGS. 6A and 68 maybe used in any application where it is required to magnetically record information contained in an electrical signal onto a recording medium, for example a magnetic tape as used in videotape or other type of magnetic recorders or in nonpercussive printing apparatus which utilizes a thin flexible band in place of the conventional printing drum.
  • a recording medium for example a magnetic tape as used in videotape or other type of magnetic recorders or in nonpercussive printing apparatus which utilizes a thin flexible band in place of the conventional printing drum.
  • the magnetic recording heads shown in FIGS. 1A and 1B and FIGS. 4A and 48 may also be utilized in these applications as well as in nonpercussive printing machines.
  • a magnetic recording head arrangement for producing on a magnetizable recording medium moving adjacent and relative thereto a permanent magnetic record of the elements of received intelligence signals, each of said signals being recorded across the width of said recording medium substantially perpendicular to the direction of movement thereof i comprising:
  • a magnetic pole structure including pole members disposed transversely of the recording ⁇ medium defining adjacent to the medium a recording gapfof substantially constant width which extends across the width of the medium, said pole structured'ecreasing 'in cross section from one edge of the medium to'th'e other to obtain a continuous gradual increase of reluctance from a minimumat said one edge to a maximum at sa'id'other edge;
  • means disposed in the magneti'c'circuit formed by sai magnetic pole structure and the recording medium, for applying to the magnetic circuit a repetitive bias signal having gradually decaying amplitude; and
  • a single conductor disposed in said magnetic pole structure proximate to and extending across the medium sub- 7 stantially parallel to said recording gap, for applying to the medium the received intelligence signals, the elements of eachsiggnal being recorded across the medium at successive porn as determined by the coincidence of members are disposed on the same side of the recording medi-,
  • first pole member is positioned on one side of the recording medium and a second pole member is positioned substantially opposite thereto on theother side of the medium, and wherein the pole members define, between the respective surfaces adjacent the medium, a recording gap.

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  • Recording Or Reproducing By Magnetic Means (AREA)
  • Printers Or Recording Devices Using Electromagnetic And Radiation Means (AREA)
US727965A 1966-11-11 1968-05-09 Magnetic recording head having constant-width recording gap subjected to decaying amplitude bias Expired - Lifetime US3549824A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB50574/66A GB1183587A (en) 1966-11-11 1966-11-11 Electrographic Apparatus
GB25608/67A GB1141726A (en) 1966-11-11 1967-06-02 A magnetic recording head

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US3549824A true US3549824A (en) 1970-12-22

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US (1) US3549824A (fr)
CH (1) CH485290A (fr)
DE (1) DE1774318A1 (fr)
FR (1) FR94962E (fr)
GB (1) GB1141726A (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4398229A (en) * 1981-08-03 1983-08-09 Eastman Kodak Company Magnetic head with versatile gap
EP0195590A2 (fr) * 1985-03-22 1986-09-24 Ampex Systems Corporation Transducteur magnétique de balayage commandé électro-magnétiquement

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3110597A1 (de) * 1981-03-18 1982-09-30 Agfa-Gevaert Ag, 5090 Leverkusen Verfahren zur aufzeichnung und wiedergabe von elektrischen signalen auf magnetische schichten in vielspurtechnik

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4398229A (en) * 1981-08-03 1983-08-09 Eastman Kodak Company Magnetic head with versatile gap
EP0195590A2 (fr) * 1985-03-22 1986-09-24 Ampex Systems Corporation Transducteur magnétique de balayage commandé électro-magnétiquement
EP0195590A3 (en) * 1985-03-22 1989-02-08 Ampex Corporation Electromagnetically controlled scanning magnetic transducer

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Publication number Publication date
DE1774318A1 (de) 1971-07-29
GB1141726A (en) 1969-01-29
CH485290A (de) 1970-01-31
FR94962E (fr) 1970-02-27

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